When operating under high currents and voltages, semiconductor modules, and in particular power semiconductor modules, generate heat, which reduces the performance and lifetime of those modules if it is not removed appropriately. In the case of power semiconductor components and modules, with correspondingly high power losses, liquid cooling is used to ensure that the heat is transported away adequately.
In the case of direct liquid cooling, the power semiconductor module has on its underside heat exchangers (for example heat sinks), which take up the heat of the components and, by direct contact with the cooling liquid, transfer it to the liquid. Consequently, the cooling liquid heats up while it flows along the underside of the module, the temperature of the cooling liquid increasingly becoming closer to the operating temperature of the module. However, the cooling effect (i.e. the heat transfer from the module to the cooling liquid) is strongly dependent on the temperature difference between the component and the cooling liquid, and consequently the module is cooled better on that side on which the (cold) cooling liquid flows in than on that side on which the (heated) cooling liquid flows out again. The components that are arranged one behind the other in the module (seen in the direction of flow of the cooling liquid) are accordingly not cooled uniformly, and therefore experience different thermal loading, which restricts the lifetime of the module as a whole to the lifetime of the component that is cooled the worst.
Previous cooling solutions have only provided longitudinal and transverse flows of the cooling liquid underneath the baseplate, longitudinal flows running along the (long) longitudinal direction and transverse flows running along the (short) transverse direction of the module. In the case of the longitudinal flow, the effect of the inhomogeneity of the temperature distribution in the cooling liquid is at a maximum, since the cooling liquid is introduced on a narrow side of the module and is carried away again on the opposite side of the module. Over the entire length (i.e. along the longitudinal sides) of the module, the cooling liquid accordingly heats up, whereby the components that are located on each side of the module on which the heated cooling liquid is carried away are cooled with warmer liquid than those on the opposite side of the module, on which the cold cooling liquid is introduced.
The solution using transverse flow solves the problem of inhomogeneity, but requires much greater volumetric flows of the cooling liquid, since the flow cross section is dictated by the (long) longitudinal side. The associated higher pumping rates are unwanted, especially in modern areas of application such as electric or hybrid vehicles.